Year:2002 | Volume:36 | Issue:1 (75)|Papers Count:12

Nowadays, polarization diversity scheme has been adopted in place of space diversity since it reduces the number of antennas in comparison with space diversity scheme and hence lowers the cost of antennas and their supporting BTS towers. The diversity gain from polarization diversity is maximized if the dual-polarized antenna has receive diversity ports that receives radiation in a cross-polarized fashion over the desired coverage area with equal field strengths and deliver it to the diversity network. Like space diversity, polarization diversity relies on the decor relation of the two receive ports to achieve diversity gain. It is customary to use a slant-45 polarization diversity antenna which consists of two independent linearly polarized dipoles or micro strip patch elements. Therefore, it is not guaranteed to deliver two nearly equal power signals to the diversity network. In this work, we have used two independent left and right circularly polarized elements instead of two independent linearly polarized elements to guarantee equal received signal power to be delivered to the diversity network. To make comparison between this new type antenna and ordinary one, correlation factor and SNR of both types are calculated. It is shown that this new type antenna, not only support common properties but also guarantee nearly equal signal power input to the diversity network.

In this paper a mathematical model is developed to simulate the effects of groins on wave induced currents in the near shore region. The model is based on the solution of depth averaged Navier Stokes equations using finite difference method. Due to the significance of wave-current interaction in the vicinity of groins, the model has the option to simulate this interaction. The model is calibrated and verified against the results of physical experiments reported by the author [1], and that of the others. The simulations are performed with and without taking the effects of wave-current interaction into account and the necessity of considering this phenomenon are evaluated.

During their operating life on site, jacket structures may be subjected to boat impacts. It is useful to know the boat impact intensity a structure can withstand without considerable damage or disruption of normal operations. Furthermore, it is advantageous to know the maximum impact intensity that could cause platform failure. This paper deals with ship impact analyses of SPD1, one of south pars field wellhead jackets located in Persian Gulf. The collision velocities are considered to be 0.5(m/s), 1(m/s) and 2(m/s). Each case was analyzed for two load cases, i.e. one representing impact on the brace and the other reflecting impact on the leg. The striking structure and struck structure are considered as one structural system connected by contact element. In order to allow for local deformation of the impacted leg or brace, a non-linear spring was used at the point of impact on the appropriate part of impacted member. The supply vessel was modeled at one end of the spring; the ship and impacted member springs were separated by a contact element as to allow rebound to occur. To account for hydrodynamic effect added mass is used. Jacket and piles are modeled together while the pile can slip axially relative to the leg. Dynamical pile-soil interaction is accounted. During simulation of impact scenario the concentrated mass, representing the displacement of the ship was prescribed with the required initial velocity. It is shown that strain hardening and large displacement play an important role in the impact response; therefore a rational collision analysis should take into account the effect of large displacement, plasticity and strain hardening. Impact velocity and impact location have significant effect on the structure response. When brace is impacted the 3-hinge mechanism becomes the predominant absorbent of plastic energy and shipside indentation remains elastic. As impact velocity increases, plastic zone is extended in impacted member section. In impact velocity recommended by API (0.5m/s) impacted leg remains elastic and plastic zone of brace section is bounded to outer fibers of section. It is recommended to use impact force derived in this study to consider the behavior of tubular members under impact loads.

In order to carry out a nonlinear structural analysis, the actual behavior of members in nonlinear range of deformations must be known and considered. In this type of analysis, the said behavior must be in conformity with experimental observations. In the structures with tubular members such as jacket type offshore structures, two types of member behavior i.e. strut and portal may be observed. In this paper a nonlinear fiber element (Post buckling Beam Column Fiber Element) for the simulation of nonlinear responses of tubular members is formulated. This element is implemented in the non-linear program DRAIN-3DX. The results of this element are compared with available experimental and analytical models. They show satisfactory result for both strut and portal members.

In this paper a novel non-parametric approach for the 3D object recognition from digital/digitized images is presented. Due to the non-deterministic behavior and complexities associated with the object recognition process, the proposed method incorporates a fuzzy reasoning strategy for the object recognition process. The proposed recognition method takes advantage of all descriptive parameters that define a 3D object in an integral manner. These are objects structural, textural and spectral attributes. The structural attributes are related to the 3D construction (such as shape, size and relief) of the object and are extracted from the generated underlying DSM. The textural information is extracted from the corresponding 2D regions in image space. 2D regions are determined using a fuzzy based region growing strategy. The spectral information is extracted using a mean value calculated for the radiometric information included in 2D regions using all available multi spectral spaces. These descriptive attributes are fused simultaneously using Mamdani and Takagi-Sugeno fuzzy inference strategy. The proposed recognition method is also embedded with training potentials. The training potentials are realized by incorporating a neuro fuzzy technique by which the originally defined membership functions can be modified. This means that the parameter definitions are automatically tuned when unrecognized objects encountered. This paper describes the implemented recognition and training strategy. This is followed by a report of the test results conducted for the evaluation of the proposed method. The tests demonstrate promising results.

The studies on vehicle body joints show their non-rigid behavior. In other words, when the body is exposed to load or forced displacement, its response is partially related to the magnitude of the flexibility of the joints between the structural members. Neglecting the joints flexibility and considering them as rigid connections may lead to substantial error in analyzing body structural stiffness. The displacement value of the joint area is remarkable compared with the displacement of the loaded point. This shows the importance of the subject for which sufficient attention must be paid if an accurate evaluation of the body behavior under different load conditions is desired. The present work investigates the elastic behavior of a T-shaped joint and renders a method for its stiffness evaluation. In this method partial displacement of the loaded point caused by joint area displacement is measured. Then the stiffness of the joint area in terms of the torque causing one radian angular displacement of the joint is calculated. Moreover, the stiffness of a T-shaped joint of a vehicle body designed and manufactured in a local vehicle maker is determined. The results pertaining displacement of the joint area show importance of the joints stiffness. At last, the experimental results are verified through finite element analysis of the model using commercial software. Comparing the results shows appropriate agreement between analytical and experimental results.

Micro heat pipes are widely used for the thermal control of spacecraft and their electronic components. In this paper the influence of linear accelerations in micro grooves has been studied. A mathematical model for predicating the minimum meniscus radius and the maximum heat transport in triangular grooves under the influence of linear acceleration is presented and method for determining the theoretical minimum meniscus radius is developed. It is shown that both, the direction and the magnitude of the acceleration have a great effect upon heat transfer capability of micro heat pipes. The analysis presented here provides a mechanism where by the groove geometry can be optimized with respect to the length of the heat pipe and direction and magnitude of linear acceleration.

Preheating in steel industries is defined as a treatment during which different steel profile is continuously heated up to the hot working temperature. One of the most important side effects in this process is surface oxidation or "scaling". Furthermore the adhesively of oxide scales on the slab surfaces is considered as a crucial factor. In the present investigation, using a new concept, the effects of chemical composition and the interface morphology on the scale adhesively of three different low carbon steels are studied. The results indicate that the presence of Si leads to interface "Fayelite" phase formation, which tends to strengthen and increase the adhesively. More over it was observed that the interface roughness would enhance the mechanical adhesively.

Zinc based alloys of the Binary system of Zn-Al have wide industrial applications, such as Bearing and Bushing. Various physical metallurgical principles of Zinc-rich alloys have been fully investigated especially, their phase transformations near the room temperature. Less attention has been paid to the Al-rich alloy (with more than 20 wt% of Zn) of the same Binary system, especially quench - ageing processes, near the room temperature. In the present article, the phase transformations of the Al based alloy (with 30 Wt% of Zn) after the quench- ageing processes, natural and artificially aged at 100°C have been investigated, by mans of Electron Microscopy (T.E.M, S.T.E.M), Techniques. It has been shown that the high temperature supersaturated α' phase is transferred to the stable η- phase by the formation of G.P Zones and two transitional phases called α'm and α"m both with the F.C.C structures.

Thermal design of vessels containing suspensions requires a proper knowledge of the heat transfer coefficient inside the vessel. A number of process vessels with reacting and non - reating systems contain suspensions which is stirred using a mechanical stirrer. The heat transfer surface is usually a jacket surrounding the vessel. The coefficient of convection heat transfer inside these vessels is influenced by several parameters such as properties of the liquid and the particles in the suspension, mean size of the suspended particles, type and dimensions of the stirrer and the revolution speed of the stirrer. In this experimental study variation of the heat transfer coefficient with all of the above parameters except the type of the liquid is investigated. Sand particles with various mean sizes are suspended in water contained in a mechanically stirred vessel. The type of stirrer chosen has been a four - blade 45³ pitch turbine stirrer. The content of the vessel is heated using an electrical coil and is cooled using a steady water flow in the jacket of the vessel. The experimental parameters were varied within the following range as: Mean particle size 0.2-0.8mm. %Wt concentration of particles 2.14-10.3 Stirrer revolution speed 700-1400 r.p.m. By performing a series of experiments, measuring the temperature at various locations in the vessel and analyzing the data gathered based on overall heat balances, the amount of the heat transfer coefficient for each experiment is determined. Finally a dimensionless correlation is derived showing the heat transfer coefficient indicated in Nusselt number as a function of Reynolds and Prandtl numbers with modified physical properties including the properties of both the liquid and the solid particles. The results of this study can be useful for the design and performance investigation of process vessels containing slurries

In order to investigate the effect of addition of whole chick pea and decocted faba bean flours on the Nutritional value, Rheological properties of dough and organoleptic properties of Barbary bread from different values of above flours at the levels of 5, 10 and 15 percent (in star flour) are used. In this research the quantities of gluten, ash, protein content, crude fat, fiber, amino acids, pH, falling number and colour of flours and farinograph, amyl graph and extensiograph properties of doughs and compressibility of breads are measured by addition of chick pea and faba bean flours in star flour. It shows an increase in protein content, minerals and fiber of star flour. Addition of 5, 10 and 15 percent of chick pea flour in star flour are accompanied by 8.2, 14.8 and 24 percent increases in protein content, respectively. While with addition of 5, 10 and 15 percent of faba bean flour in star flour that are accompanied by 12, 20.3 and 32.5 percent increases protein content. The incorporation of chick pea flour in star flour causes crude fat increases. By addition of chick pea and faba bean flour in star flour all of the essential aminoacids, with the exception of sulphur containing amino acids (methionine and cystine), are increased. By addition of above flour in star flour, resistance of dough, maximum resistance to extension, extensibility and energy of dough are decreased. The incorporation of 0.2 percent lecithin causes rheological properties of dough to improve. Addition of chick pea and faba bean flours in star flour causes gas production of dough at different hours of fermentation to increase. Faba bean flour is significantly more effective on yeast-gas production than chickpea flour. The organoleptic evaluation of all produced Barbary bread shows that by addition of chick pea and faba bean flours in star flour, overall acceptability of all breads, with the exception of a bread containing 5 percent of chick pea, decreases. By addition of 0.2 percent lecithin, overall acceptability of all breads, (with the exception of bread containing 15 percent faba bean flour) shows the same level as the control Bread. The statistical analysis of results confirms this issue. By addition of chick pea and faba bean flours in star flour, compressibility of bread with respect to the control bread is decreased or texture of crumb is hardened. By addition of 0.2 percent lecithin, compressibility of all bread improves, and texture of crumb softens. Breads containing 10 and 15 percent faba bean flours possesses finer texture of crumb than the control bread

Determination of mass transfer coefficient, Reynolds number, Stanton number and other hydrodynamic parameters of a fluid are very important in heat transfer and fluid dynamic science. Measuring the above parameters need very precise instruments which are very expensive. Therefore, in this research an attempt was made to use electrochemical theories together with the uniform corrosion rate of copper metal in water to establish a relationship between mass transfer coefficient and corrosion rate. From the obtained relationship, determination of some hydrodynamic parameters of fluid was investigated. The result of this research was in a good agreement with the results of other investigators that obtained the hydrodynamic parameters by different methods.